1. Field of the Invention
The present invention relates to an image pickup apparatus, a radiation image-pickup apparatus, and a radiation image-pickup system. More specifically, the invention relates to an image pickup apparatus for use in a radiation image-pickup apparatus and a radiation image-pickup system.
2. Description of the Related Art
In recent years, a radiation image-pickup apparatus including a flat panel detector (hereinafter abbreviated to an FPD) formed of a semiconductor material is coming into practical use as an image pickup apparatus for use in radiographic medical diagnostic imaging and nondestructive examination. The pixels of the FPD each include at least a transducer that converts radiation or light to electrical charge and a switching element that outputs an electric signal corresponding to the electrical charge generated by the transducer. Such an FPD is provided with a drive circuit that drives a plurality of pixels and a read circuit that reads the electric signals output from the plurality of pixels. The image pickup apparatus including the above FPD is provided with a signal processing unit that processes the image signals from the read circuit and transmits the image signals to the exterior or receives control signals from the exterior; a power supply unit that applies various biases to the plurality of pixels, the drive circuit, and the read circuit; and a control unit that controls the various components according to the control signals. For example, in a medical image diagnosis, such an image pickup apparatus is used as a digital image pickup apparatus for still-image acquisition, such as common image acquisition, and moving-image acquisition, such as radiation image pickup apparatus. For this image pickup apparatus, various configurations have been proposed, for example, a configuration in which the supply of voltage to the power supply unit, the transmission of control signals to the control unit, and the transmission of image signals from the signal processing unit are performed using cables and a configuration in which supply voltage is supplied to the power supply unit from a battery or the like and the transmission and reception of the control signals and the image signals are performed by radio. For either configuration, various measures have been taken in view of increasing the life of the FPD and reducing the power consumption of the image pickup apparatus.
In view of the above, US Unexamined Patent publication 2002/0044211 and US Unexamined Patent publication 2006/0169907 disclose a configuration in which a plurality of standby modes including a first standby mode in which the power consumption is lower than an image-acquisition mode and a second standby mode in which the power consumption is lower than that of the first standby mode and the image-acquisition mode and the plurality of standby modes are switched.
However, even if the technology disclosed in US Unexamined Patent publication 2002/0044211 and US Unexamined Patent publication 2006/0169907 is executed, the life of the FPD or the image pickup apparatus can be affected when power supply to the FPD is stopped into the standby state, as in the above-described standby mode, or power supply to the entire image pickup apparatus is stopped into a stopped state. When the FPD or the image pickup apparatus enters the standby state or the stopped state, there is a risk of causing degradation of the characteristic of the pixels due to long-time application of voltage to the transducers and the switching elements and fluctuations in the characteristic of the read circuit due to excessive electrical charge flowing to the read circuit.